1. Field of the Invention
The present invention relates to improved methods of cementing subterranean zones penetrated by well bores using biodegradable dispersants.
2. Description of the Prior Art
Subterranean zones penetrated by well bores are commonly sealed by hydraulic cement compositions. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipes such as casing and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein which supports and positions the pipe string in the well bore and seals the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also utilized in a variety of cementing operations such as sealing highly permeable zones or fractures in subterranean zones, plugging cracks or holes in pipe strings and the like.
Dispersing agents are commonly included in hydraulic cement compositions used for cementing subterranean zones. The dispersing agents reduce the rheologies of the cement compositions, i.e., the apparent viscosities and other properties of the cement compositions, as well as reducing the water content of the cement compositions. The reduction of the rheology of a cement composition allows the cement composition to be pumped with less friction pressure and less pump horse power. In addition, the lower rheology often allows the cement composition to be pumped in turbulent flow. Turbulent flow characteristics are desirable when pumping cement compositions in wells in that drilling fluid is more efficiently removed from surfaces in the well bore as the drilling fluid is displaced by the cement compositions being pumped. The inclusion of dispersing agents in cement compositions is also desirable in that the presence of the dispersing agents reduces the water required for preparation of the cement compositions. Cement compositions having reduced water content set into cement masses having improved compressive strengths.
A number of dispersing agents have been utilized heretofore in cement compositions, particularly in cement compositions used for primary and remedial cementing in oil and gas wells. However, most of such dispersing agents are also strong cement composition set retarding agents which is often undesirable. That is, the presence of such a dispersant in a cement composition prevents the cement composition from setting for a relatively long period of time which is often costly or otherwise detrimental. While various other cement dispersants have been developed and used which do not substantially increase the setting time of cement compositions, they are not environmentally acceptable, especially in offshore operations in that they do not undergo complete biodegradation in the environment and cause damage to aquatic and other life therein. Thus, there are continuing needs for improved biodegradable cement composition dispersants and improved cement compositions containing such dispersants.
The present invention provides improved methods and compositions for cementing subterranean zones penetrated by well bores which meet the needs described above and overcome the deficiencies of the prior art. The methods of the invention for cementing subterranean zones penetrated by well bores basically comprise the following steps. A cement composition that comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehydes and sulfur-containing acids or their salts is prepared or provided. The cement composition is placed in the subterranean zone to be cemented, and then the cement composition is allowed to set into a solid mass therein.
A well cement composition of this invention basically comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehyde and sulfur-containing acids or their salts.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
The methods of cementing a subterranean zone penetrated by a well bore in accordance with the present invention comprise the following steps. A cement composition is prepared or provided that comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant. The cement composition is placed in a subterranean zone to be cemented and the cement composition is then allowed to set into a solid mass therein.
The cement compositions of this invention basically comprise a hydraulic cement, sufficient water to form a slurry, and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehydes and sulfur-containing acids or their salts.
The polyamide component of the graft copolymer is a natural polyamide. Examples of such natural polyamides which can be utilized include, but are not limited to, casein, gelatin, soy protein, polyaspartic acid, collagens, bone binders, blood albumins, and their degradation products. Of these, gelatin is generally preferred. The polyamide component is generally present in the graft copolymer in an amount in the range of from about 5% to about 80% by weight, more preferably in an amount of from about 10% to about 60% by weight.
Examples of the aldehyde component of the graft copolymer include, but are not limited to, paraformaldehyde, paraldehyde, formaldehyde, acetaldehyde, and glyoxal. Of these, formaldehyde is generally preferred. The aldehyde component of the graft copolymer is generally present therein in an amount in the range of from about 5% to about 90% by weight, more preferably in an amount from about 10% to about 70% by weight.
Examples of the sulfur-containing acid or salt thereof component of the graft copolymer include, but are not limited to, inorganic sulfite salts, hydrogen sulfite, bisulfites of alkaline earth metals, aluminum, iron and ammonium, napthalenesulfonic acid and its salts, and benzenesulfonic acid and its salts. Of these, inorganic sulfite salts are preferred with sodium sulfite being the most preferred. The sulfur-containing acid or salt component of the graft copolymer is present therein in an amount in the range of from about 5% to about 60% by weight, more preferably in an amount from about 15% to about 40% by weight.
The side chain formed from aldehydes and sulfur-containing acids or their salts can also include at least one additional compound selected from the group consisting of ketones, aromatic alcohols and aminoplastic-forming agents such as dicyanodiamide, urea derivatives, aminio-s-triazines, melamines, and melamine derivatives. Of these, ketones are preferred such as acetone, 2-propanone, 2-butanone, and pyruvic acid. Of these, acetone is the most preferred. When included, the additional compound in the side chain is present in the graft copolymer in an amount in the range of from about 5% to about 85% by weight, more preferably in an amount of from about 10% to about 70% by weight.
The biodegradable cement dispersant is prepared by graft polymerization at temperatures between xe2x88x9210xc2x0 C. and 250xc2x0 C. The polymerization is conducted in the presence of a solvent such as water or dimethyl sulfoxide. Alternatively, the dispersant can be prepared by thermal treatment.
A particularly preferred biodegradable cement graft copolymer dispersant comprises gelatin present in an amount of about 42% by weight, a 37% by weight solution of formaldehyde present in an amount of about 22% by weight, sodium sulfite present in an amount of about 18% by weight, and acetone present in an amount of about 18% by weight. The water soluble biodegradable polyamide graft copolymer useful in accordance with the present invention is described in greater detail in German Patent Application No. DE 103 14 354.8 entitled WATER-SOLUBLE BIODEGRADABLE POLYAMIDE-BASED COPOLYMERS AND THEIR USE filed on Mar. 31, 2003 (inner priority Dec. 11, 2000 for DE 102 57 701.3) which is incorporated in its entirety herein by reference thereto.
Examples of hydraulic cements that can be utilized in the cement compositions of this invention include, but are not limited to, Portland cements, slag cements, pozzolana cements, gypsum cements, aluminous cements and silica cements. Portland cements and their equivalents are generally preferred for use in accordance with the present invention. Portland cements of the types defined and described in API Specification for Materials and Testing for Well Cements, API Specification 10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly preferred.
The water in the cement compositions can be fresh water or salt water. The term xe2x80x9csalt waterxe2x80x9d is used herein to mean unsaturated salt solutions and saturated salt solutions including brines and seawater. The water is present in the cement compositions in amounts sufficient to form a pumpable slurry. Generally, the water is present in an amount in the range of from about 30% to about 63% by weight of hydraulic cement in the compositions.
The water soluble biodegradable graft copolymer cement dispersant is generally present in the cement compositions of this invention in an amount in the range of from about 0.25% to about 5% by weight of cement therein, more preferably in an amount of about 1%.
Examples of the preparation of various biodegradable graft copolymer cement dispersants of this invention include, but are not limited to, the following:
(No. 1) A biodegradable graft copolymer cement dispersant comprising casein, formaldehyde, sodium sulfite, and acetone is prepared as follows. 20 grams of casein is dissolved in 210 grams of water. 17.5 grams of sodium sulfite and 16.5 grams of acetone are added to the casein solution. The solution is heated to 140xc2x0 F. followed by slow addition of 80 grams of 30% aqueous formaldehyde solution. The solution is stirred for two hours at 158xc2x0 F. and the pH of the reaction solution is adjusted to 7 with formic acid. The solution is then concentrated to half the original volume by vacuum distillation to remove methanol produced by the competing Canizarro reaction.
(No.2) A biodegradable graft copolymer cement dispersant comprising gelatin, formaldehyde, sodium sulfite and acetone is prepared as follows. 240 grams of gelatin are dissolved in 600 grams of water containing 100 grams of sodium sulfite and 100 grams of acetone. Following the addition of 350 grams of a 37% by weight aqueous formaldehyde solution, the mixture is heated to 140xc2x0 F. The pH of the solution is adjusted to 7 with formic acid and heated for two hours at 176xc2x0 F. The reaction solution is distilled in a vacuum to remove methanol.
(No.3) A biodegradable graft copolymer cement dispersant comprising casein, sodium sulfite, acetone and sodium pyrosulfite is prepared as follows. 100 grams of sodium sulfite and 100 grams of acetone are dissolved in 250 grams of water. The solution is heated to 140xc2x0 F. Then 467 grams of 30% aqueous formaldehyde solution are added. The reaction solution is stirred for 40 minutes at 158xc2x0 F. At the end of 40 minutes, 7.26 grams of sodium pyrosulfite are added and the solution is stirred for an additional 30 minutes. The pH of the solution is adjusted to 7.0 with formic acid. The solution is distilled under vacuum to remove methanol. The residual solution is diluted to 6 liters with distilled water and 340 grams of casein. The resulting polymer solution is dried whereby grafting of the backbone takes place.
(No.4) A biodegradable graft copolymer cement dispersant comprising soy protein, formaldehyde, sodium sulfite, and acetone is prepared as follows. 100 grams of soy protein are added to 600 grams of water. The pH of the solution is adjusted to about 13 with sodium hydroxide. To this solution are added 104 grams of sodium sulfite and 98 grams of acetone. The mixture is then heated to 176xc2x0 F. To the heated solution 356 grams of 30% aqueous formaldehyde solution are added drop wise with vigorous agitation. The pH of the solution is adjusted to 7 with formic acid. Methanol produced by a competing Canizarro reaction is completely distilled off under vacuum to produce the condensation product.
(No.5) A biodegradable graft copolymer cement dispersant comprising polyaspartic acid, acetaldehyde, sodium sulfite and pyrocatechol is prepared as follows. 15.9 grams of polyaspartic acid is dissolved in 100 grams of water. The solution is cooled to 35.6xc2x0 F. To the chilled solution is added 34.8 grams of sodium sulfite and 36 grams of pyrocatechol. Then, 40.9 grams of acetaldehyde is added drop wise taking precaution not to raise the temperature of the solution above 53.6xc2x0 F. Upon completion of the addition, the temperature is raised to 167xc2x0 F. and agitated for two hours at that temperature. The solution is cooled to 68xc2x0 F. and the pH is adjusted to 7 by formic acid. The solution is concentrated to half its volume under vacuum.
(No.6) A biodegradable graft copolymer cement dispersant comprising gelatin, glyoxal and urea is prepared as follows. 39.77 grams of gelatin are added to 100 milliliters of dimethyl sulfoxide. To the solution is added 17.4 grams of sodium sulfite and 16.4 grams of urea with stirring. The mixture is heated to 140xc2x0 F., followed by the addition of 6.9 grams of 40% aqueous glyoxal solution. The reaction mixture is then heated to 167xc2x0 F. and held at that temperature for two hours. The dimethyl sulfoxide is then removed under reduced pressure.
(No.7) A biodegradable graft copolymer cement dispersant is comprising polyaspartic acid, formaldehyde, sodium pyrosulfite and melamine is prepared as follows. 150 grams of 30% aqueous formaldehyde solution is heated to 86xc2x0 F. Then, 63 grams of melamine and 50 grams of sodium pyrosulfite are added, followed by 95 grams of a 15% solution of sodium hydroxide. To this solution is added 280 grams of water.
The pH of the solution was adjusted to 3 with sulfuric acid. 70 grams of a 40% aqueous solution of polyaspartic acid was then added to the solution. The solution is raised to a temperature of 160xc2x0 F. and held at that temperature for two hours. The reaction solution is concentrated to ⅓ of its original volume with reduced pressure and a temperature of 176xc2x0 F. The solution is cooled and the pH is adjusted to 7 with sodium hydroxide.
In addition to the above described biodegradable graft copolymer cement dispersants numerous other dispersants of this invention can be prepared using the various chemical components described herein.
A preferred method of cementing a subterranean zone penetrated by a well bore comprises the steps of: (a) preparing or providing a cement composition that comprises a hydraulic cement, sufficient water to form a slurry and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed from aldehydes and sulfur-containing acids or their salts; (b) placing the cement composition in the subterranean zone to be cemented; and (c) allowing the cement composition to set into a solid mass therein.
A preferred well cement composition of this invention comprises: a hydraulic cement; sufficient water to form a slurry; and a water soluble biodegradable cement dispersant comprising a polyamide graft copolymer containing at least one side chain formed of aldehydes and sulfur-containing acids or their salts.